Adverse childhood experiences (ACEs) refer to stressful or traumatic events encountered during childhood, specifically defined as incidents occurring before the age of 18 (1). Over 60% of adults report experiencing at least one adverse childhood experience, and 17% report four or more ACEs. ACEs persistently impact adverse health outcomes throughout an individual’s life, contributing to lower educational attainment, significant causes of adult mortality and influencing various psychosocial outcomes linked to mental illness and poor health, as well as substantial financial costs (2–6).

In China, the escalating aging population has brought about heightened concerns regarding cognitive decline (7). This decline among the older adults can lead to various adverse outcomes, including health complications, reduced social interaction, heightened safety hazards, greater medical complexities, and financial strains (8). Studies have indicated a connection between ACEs and cognitive impairment in adulthood, particularly impacting memory, processing speed, and executive functions, even in later life stages (9–13). Further investigations into the enduring cognitive consequences of specific ACEs could shed light on the specificity and pathways linking individual ACEs to cognitive functions in later life. Some studies have adopted a mediation framework to explore these associations. By examining these potential pathways, invaluable insights could be gained to develop more effective intervention and prevention strategies aimed at mitigating the risks associated with cognitive impairment.

Numerous studies have already found that individuals who have experienced ACEs are more likely to have lower educational attainment (6, 14). This early exposure to ACEs has been linked to a decline in educational achievement, contributing to variations in cognitive skills that manifest in early adulthood and persist into older age, thereby increasing the risk of age-associated cognitive decline and late-life dementia (15). Moreover, recent research has identified specific adverse experiences that may further exacerbate cognitive declines by influencing educational attainment. For instance, one study demonstrated a robust and enduring indirect association between parental substance abuse and poorer cognitive function in later life, mediated through educational level (16). Similarly, Halpin et al. observed that heightened childhood adversity could amplify susceptibility to cognitive impairment by shaping the early educational experiences of older adults (17). Additionally, Burr et al. found that adult loneliness partially mediated the relationship between childhood friendship experiences and cognitive function in later life (18). These findings collectively underscore the intricate relationship between ACEs, educational level, and cognitive function across the lifespan. They highlight the importance of considering the long-term consequences of ACEs on educational outcomes and cognitive health in later life.

Loneliness, characterized as the perception of social isolation or the subjective feeling of being alone (19), represents a significant public health concern that often goes unrecognized or trivialized (20). Considering the escalating number of older adults, it becomes crucial to acknowledge the detrimental effects of loneliness, as revealed in both animal models and longitudinal human investigations (21–23). Substantial studies have found that loneliness was associated with objective social isolation, depression, or poor social skills, cognitive impairment and premature mortality (23–25). Emerging evidence have suggested that those who have been exposed to ACEs are more likely to have the feeling of loneliness (26, 27). For example, individuals who are exposed to ACEs report low self-esteem and problems with emotional regulation, which may lead to encounter challenges in experiencing pleasure, contentment, and happiness. Lin et al. found that ACEs were associated with feeling of loneliness (FOL) trajectory, which play a mediating role between ACEs and problematic internet use in young adults (28). Besides, the mediating role of loneliness have been identified between ACEs and pain, problematic internet abuse and depressive symptoms (28–30). Therefore, one potential explanation for the link between ACEs and cognitive impairment is exposure to adverse events in early life, which can lead to increased feelings of loneliness (FOL) later in life, thus resulting in greater impairment of cognition. However, there remains a scarcity of research delving into the precise mechanisms through which ACEs elevate the risk of cognitive deficits, including factors like educational level and subjective FOL. Exploring these potential pathways could provide valuable insights for the development of more effective intervention and prevention strategies aimed at mitigating the risks associated with cognitive impairment.

There is a lack of studies examining the association between ACEs and the decline of cognitive functioning in later life through a sequential mediating pathway. There could exist a direct relationship between ACEs and cognition. Alternatively, depending on the strength of the mediators, there may be an indirect pathway involving educational level and FOL. Through these indirect pathways, it is possible to elucidate the mechanisms through which ACEs contribute to an elevated risk of cognitive impairment. Drawing from the literature discussed earlier, it can be inferred that the cumulative effect of ACEs may increase the likelihood of lower cognitive function among older individuals. Consequently, we have formulated four hypotheses to guide our investigation:

Figure 1 illustrates the proposed research model for the current study.

Therefore, leveraging the unique longitudinal cohort of the China Health and Retirement Longitudinal Study (CHRLS), the current aimed to (1) examine the association between ACEs and education level, FOL and cognitive function in older adults; (2) investigate the connection between FOL and cognitive function; and (3) determine if education level and FOL sequentially mediated the association between ACEs and cognitive function.

Building upon a large cohort study, this research delved into exploring the connection between ACEs and cognition. Additionally, it examined the extent to which education level and the FOL sequentially mediate this association. There are several noteworthy findings to highlight. First, ACEs were linked to diminished educational level, heightened FOL, and lower cognitive function. Furthermore, potential indirect pathways were identified involving the education and FOL between ACEs and cognitive function. In summary, our findings contribute to the existing literature by presenting new evidence supporting the role of educational level and FOL as mediators in the relationship between ACEs and cognition.

Consistent with previous research, our finding showed that ACEs were inversely related with education level. Giovanelli et al. discovered that individuals who experienced one or more conventional or expanded ACEs during early childhood were associated with fewer years of education, a diminished likelihood of achieving a bachelor’s degree or higher, and a decreased likelihood of obtaining an associate’s degree or higher. And they proposed that youths at higher risk can benefit most from early intervention for reducing ACE-related disparities (14). Numerous studies suggest that ACEs have significant impacts on individuals’ health and development, including affecting learning ability in school (32, 33), having a negative impact on children’s cognitive development (34), limiting educational resources and opportunities, and influencing individuals’ emotional regulation and coping strategies (35, 36). These effects collectively make it challenging for individuals to effectively deal with academic and life pressures. The cumulative impact of ACEs can create barriers to educational success and overall well-being.

Additionally, our examination also revealed that ACEs were positively associated with subjective FOL. Lin et al. found that individuals exposed to ACEs were at a higher risk of experiencing an increasing trajectory of FOL, with a dose–response relationship existing between the two (28). In the context of subjective experiences of social feelings, one review has highlighted the involvement of neurotransmitters, neurohormonal modulators, and specific brain regions in the mechanisms underlying loneliness (37). Furthermore, Brent and Silverstein et al. further proposed a link between early stress or adversity and the influence on oxytocin release and signaling (38). Oxytocin, known for its impact on interpersonal processes, affiliation, and feelings of love and trust, establishes a logical connection. This early influence may become deeply embedded in the life course, exerting enduring and long-term effects (39).

Emerging evidence showed that the long-lasting effect has been recognized that ACEs have a detrimental impact cognitive function in adults (31, 40). Prior researches investigated the association between ACEs and objective cognition (41, 42), which imply that adverse experiences in early life contribute to inferior cognitive outcomes as individuals age. One study, utilizing data from the English Longitudinal Study of Aging, demonstrated a subtle association between ACEs and memory decline over a ten-year period, spanning from middle to older age (42). Another study, which concentrated on older adults in rural South Africa, discovered a correlation between environmental ACEs, such as cohabiting with someone experiencing psychopathology (substance abuse or mental health challenges), and lower memory scores (43). There may be several potential mechanisms underlying the association between ACEs and cognitive impairment. Exposure to early-life adversity has crucial impact on brain development (44, 45). Specially, in animal models, there is direct evidence illustrating that stress during early life stages triggers structural, functional, and epigenetic alterations in brain regions linked to cognition. Notably, this includes a decrease in hippocampal volume, which has been associated with cognitive impairments, particularly memory deficits (46). These findings suggest that ACEs, education level and FOL should be taken into account as potential factors in measures of cognitive reserve, with the potential to reduce cognitive reserve.

The correlation between ACEs and cognition is mediated by both educational level and FOL. More precisely, individuals who experienced adverse events in their early lives were inclined to have a lower level of education, subsequently experiencing a heightened sense of FOL. This, in turn, elevated their likelihood of experiencing cognitive impairment. In general, both animal models and human studies have profoundly enriched our understanding of the neurodevelopmental mechanisms underlying the association between ACEs and the neural and behavioral phenotypes that result from a complex interplay between environmental, genetic, and epigenetic factors (47). Evidence indicated that early life adversity can impact life course development, including brain development, consequently leading to diminished cognitive, academic and behavioral performance and lower education attainment (6, 48). Moreover, individuals with lower levels of education in Latvia tend to experience higher levels of loneliness (49). This heightened loneliness is subsequently associated with lower scores in composite cognitive score, memory (immediate and delayed recall), verbal fluency, and backward digit span (50). Research findings highlight various measures of social isolation in long-term care settings and illuminate the contextual components that are correlated with a decrease in loneliness among older adults (51, 52). These measures may help to alleviate the cognition decline in older adults.

Our research possesses several limitations that should be acknowledged. Firstly, we did not thoroughly elucidate the relationship between the various components of ACEs and cognition. Secondly, the measures of ACEs exposure in our study utilized binary response options, which limited the exploration of adversity dimensions such as frequency, severity, duration, ages when it occurred, and the degree of psychological effects at the time. Employing more detailed and precise measures of ACEs may be essential to obtain accurate estimates of the relationships between ACEs and memory decline. Thirdly, the assessment of loneliness relied on a single item from ICSD-10. Future studies could enhance accuracy by utilizing structural questionnaires to evaluate the intricacies of FOL. For future research, to enhance the generalizability of findings and mitigate recall bias, incorporating diverse racial and cohort populations could be beneficial.

ACEs emerge as reliable predictors for educational level, the FOL, and cognitive function. Notably, chain mediation analyses revealed a novel underlying mechanism in the relationship between ACEs and cognitive function among the older population. ACEs serve as effective predictors for cognition by influencing educational level and the FOL. These findings are instrumental in early identification of individuals at risk for poor cognitive impairment, enabling interventions to exert the maximum impact on preventing or delaying cognitive and functional decline. Interventions aimed at optimizing cognitive health in the older adults and preventing future cognitive deficits should carefully consider the potential roles of ACEs, educational level, and the FOL within the relevant population.

The original contributions presented in the study are included in the article/Supplementary material. All data from CHARLS were accessible to the public through the website (http://charls.pku.edu.cn/).

This study was based on publicly available datasets. Ethical review and approval was not required for the study, in accordance with the local legislation and institutional requirements. The datasets are accessible for download on the CHARLS homepage at http://charls.pku.edu.cn/en. Approval for the CHARLS survey project was granted by the Biomedical Ethics Committee of Peking University, and all participants were required to provide informed consent through signing.

XD: Writing – review & editing, Writing – original draft, Validation, Resources, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. MX: Writing – review & editing, Writing – original draft, Visualization, Validation, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. YW: Writing – original draft, Resources, Methodology, Investigation, Funding acquisition, Conceptualization. JC: Writing – original draft, Software, Methodology, Investigation, Funding acquisition, Data curation, Conceptualization. MZ: Writing – review & editing, Visualization, Validation, Supervision, Project administration, Methodology, Conceptualization. QW: Writing – review & editing, Validation, Supervision, Project administration, Methodology, Funding acquisition, Conceptualization.